INFLUENCE OF THE AERATION AND PH ON THE X YLOSE FERMENTATION TO ETHANOL BY PICHIA-STIPITIS

The conversion of xylose into ethanol by Pichia stipitis was investiga ted under different degrees of oxygenation using several combinations of agitation rates and ratios between volume of flasks and volume of t he medium (V(F)/V(M)). The influence of pH upon this bioconversion was also studied. Ethanol yields were found to be dependent on the aerati on conditions used. Higher yields were achieved for flasks agitaded at 100 and 150 rpm in which the V(F)/V(M) ratios were 5.0 and 2.5, respe ctively. Under such conditions, it was obtained ethanol yields in the average of 0.36 g/g which corresponds to 70% of the theorical value. N o significant difference on the process performance was observed for t he various pH tested. However, a slight better yields and productiviti es were attained when the initial pH was set up to 4.5.